This invention relates to cell biology and more specifically to the control of cell proliferation.
Proteoglycans are proteins that carry one or more glycosaminoglycan chains. The known proteoglycans carry out a wide variety of functions and are found in a variety of cellular locations. Many proteoglycans are components of extracellular matrix, where they participate in the assembly of cells and effect the attachment of cells to the matrix.
Decorin, also known as PG-II or PG-40, is a small proteoglycan produced by fibroblasts. Its core protein has a molecular weight of about 40,000 daltons. The core has been sequenced (Krusius and Ruoslahti, Proc. Natl. Acad. Sci. USA 83:7683 (1986); Day et al. Biochem. J. 248:801 (1987), both of which are incorporated herein by reference) and it is known to carry a single glycosaminoglycan chain of a chondroitin sulfate/dermatan sulfate type (Pearson, et al., J. Biol. Chem. 258:15101 (1983), which is incorporated herein by reference). The only previously known function for decorin is binding to type I and type II collagen and its effect on the fibril formation by these collagens (Vogel, et al., Biochem. J. 223:587 (1984); Schmidt et al., J. Cell Biol. 104:1683, (1987)). Two proteoglycans, biglycan (Fisher et al., J. Biol. Chem. 264:4571 (1989)) and fibromodulin, (Oldberg et al., Embo J. 8:2601, (1989) have core proteins the amino acid sequences of which are closely related to that of decorin and they, together with decorin, can be considered a protein family. Each of their sequences is characterized by the presence of a leucine-rich repeat of about 24 amino acids. Several other proteins contain similar repeats. Together all these proteins form a superfamily of proteins (Ruoslahti, Ann. Rev. Cell Biol. 4:229, (1988); McFarland et al., Science 245:494 (1989)).
Transforming growth factor xcex2""s (TGFxcex2) are a family of multi-functional cell regulatory factors produced in various forms by many types of cells (for review see Sporn et al., J. Cell Biol. 105:1039, (1987)). Five different TGFxcex2""s are known, but the functions of only two, TGFxcex2-1 and TGFxcex2-2, have been characterized in any detail. TGFxcex2""s are the subject of U.S. Pat. Nos. 4,863,899; 4,816,561; and 4,742,003 which are incorporated by reference. TGFxcex2-1 and TGFxcex2-2 are publicly available through many commercial sources (e.g. R and D Systems, Inc., Minneapolis, Minn.). These two proteins have similar functions and will be here collectively referred to as TGFxcex2. TGFxcex2 binds to cell surface receptors possessed by essentially all types of cells, causing profound changes in them. In some cells, TGFxcex2 promotes cell proliferation, in others it suppresses proliferation. A marked effect of TGFxcex2 is that it promotes the production of extracellular matrix proteins and their receptors by cells (for review see Keski-Oja et al., J. Cell Biochem 33:95 (1987); Massague, Cell 49:437 (1987); Roberts and Sporn in xe2x80x9cPeptides Growth Factors and Their Receptorsxe2x80x9d [Springer-Verlag, Heidelberg] in press (1989)).
While TGFxcex2 has many essential cell regulatory functions, improper TGFxcex2 activity can be detrimental to an organism. Since the growth of mesenchyme and proliferation of mesenchymal cells is stimulated by TGFxcex2, some tumor cells may use TGFxcex2 as an autocrine growth factor. Therefore, if the growth factor activity of TGFxcex2 could be prevented, tumor growth could be controlled. In other cases the inhibition of cell proliferation by TGFxcex2 may be detrimental, in that it may prevent healing of injured tissues. The stimulation of extracellular matrix production by TGFxcex2 is important in situations such as wound healing. However, in some cases the body takes this response too far and an excessive accumulation of extracellular matrix ensues. An example of excessive accumulation of extracellular matrix is glomerulonephritis, a disease with a detrimental involvement of TGFxcex2.
Thus, there exists a critical need to develop compounds that can modulate the effects of cell regulatory factors such as TGFxcex2. The present invention satisfies this need and provides related advantages.
The present invention provides a method of inhibiting an activity of a cell regulatory factor comprising contacting the cell regulatory factor with a purified polypeptide, wherein the polypeptide comprises a cell regulatory factor binding domain of a protein and wherein the protein is characterized by a leucine-rich repeat of about 24 amino acids. In a specific embodiment, the present invention relates to the ability of decorin, a 40,000 dalton protein that usually carries a glycosaminoglycan chain, to bind TGFxcex2. The invention also provides a novel cell regulatory factor designated Morphology Restoring Factor, (MRF). Also provided are methods of identifying, detecting and purifying cell regulatory factors and proteins which bind and affect the activity of cell regulatory factors.